I think the fthrow buff was good, to me it is equivalent to him getting a weight boost when you look at it this way;
When coming up against Marios usmash, the difference between Mewtwo dying to it and Mario himself is about 18%. (Mewtwo dies at 102%, mario at 120% I jest tested it what a guess lol). It's fair to suggest that in any given stock a character is going to get grabbed say, 3-4 times.
If Mewtwo uses fthrow as his damage-racking throw, he does 47% (including staling) while if he goes for his next best option which would be 1 uthrow, 3x bthrow to not stale the uthrow, that does 40%. So he has gained 7% extra on the enemy for free.
I look at smash bros like this;
Outside of time outs, the game has only one win condition; you take the enemies stocks before they take theirs. I dont care how early a character can KO, what their weight is, combos or anything. Everything combined including all the frame data and playstyle optimisation leads to one single factor which is was the the likelihood of character A taking 2/3 stocks before character B does.
When Mewtwo gains 7% extra for free every stock it makes his ability to take the enemies stocks sooner. This is a very big deal in a race to get 2/3 first.
If Mewtwo was given a buff such that he now survives 7% longer, people would obviously be happy about that, its a buff. Now what if for example Mario got nerfed to now die 7% earlier? Thats clearly a nerf. Yet, isn't this literally the exact same thing as Mewtwo KO'ing 7% earlier and by extension, the exact same thing as Mario reaching KO% 7% earlier than normal as he took that much extra damage for free?
Since Mewtwo can apply this to every matchup, that extra ~7% per stock directly affects the likelihood in Mewtwo taking the stock first because the enemy now reaches KO range sooner. Remembering that I don't care at what % mewtwo dies, I only care about him taking 2/3 stocks before the enemy does. Again, this is literally the exact same as receiving a weight buff which would make Mewtwo reach KO % later. Whether it is Mewtwo dying later or killing earlier it is the same sort of buff.
To me, that buff is the equivalent of putting him above sheiks weight tier.
I agree the buff isn't addressing his bigger problems, but I ride that fthrow buff as far as it takes me.